Frequency synthesizers may be used to generate high frequency signals based on a lower frequency reference signal. For example, FIG. 1 shows a block diagram of a conventional phase-locked loop (PLL) circuit configured as a frequency synthesizer 100. Synthesizer 100 includes a phase and frequency detector (PFD) 102, a charge pump 104, a loop filter 106, a voltage-controlled oscillator (VCO) 108, and a frequency divider (DIV) 110. A master oscillator (e.g., crystal oscillator) may provide an input (X) to be used as a reference clock signal by the synthesizer 100. The PFD 102 compares the relative timing (e.g., phase difference) between the edges of the reference signal X and a feedback signal (FB) to generate “up” (UP) and “down” (DN) control signals. Charge pump 104 converts the UP and DN control signals to a charge (QC) that is proportional to the phase difference of signals X and FB. The charge QC is filtered (e.g., integrated) by the loop filter 106 and provided as a control voltage (VC) to the VCO 108. The VCO 108 then generates a local oscillator signal (LO) having a frequency based on the control voltage VC. The local oscillator signal LO is passed through a frequency divider 110 (e.g., to scale the frequency of LO to that of X) and fed back into the synthesizer 100 as the feedback signal FB.
Frequency synthesizers are often found in the analog front-end (AFE) of communications devices, and may be used for transmitting and/or receiving data signals. More specifically, a conventional frequency synthesizer may be coupled to both a transmit (TX) chain of the AFE and a receive (RX) chain of the AFE. Along the TX chain, the local oscillator signal LO may be used to up-convert an outgoing data signal to a carrier frequency. Along the RX chain, the local oscillator signal LO may be used to down-convert a received carrier signal to a frequency suitable for processing by the communications device. A modern communications device may enter a low-power (e.g., “sleep”) mode wherein the device does not transmit any data, and only periodically enables reception of broadcast data (e.g., beacon frames containing DTIM information) for purposes of maintaining a connection with a corresponding network and/or device.